Saturable core reactor system



Dec. 31, 1957 u. LAMM 2,818,545

SATURABLE CORE REACTOR SYSTEM Filed Sept. 20, 1952 Fig/ / IRON STEEL c K /A 1n van for. U110 La mm United. States Patent i SATURABIJE" GORE REACTONSYS'IEM Uno Lamm, IIudvika, Sweden, assignor to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, :1 corporation'of Sweden Application'September'20; .1952, SerialiNo. 310,712

Claimspriority, application Sweden'Septmber '22; I951 'Claims. (Cl. 323*89) The object of the present invention is to provide an improvement of'a transductor (i. e. a presaturated-reactor) to obtain a remaining alteration of a quantity controlled by a temporarily-acting controlcurrent.

Transductors' as well as electron-tubes belongto a type of control apparatus in which the-output quantity follows the variations of the input quantity andthu-s returns to some fixed value when the input quantity disappears. When transductors have previously been used in cases when it is desired to obtain an output quantity following an adjustable input quantity but remaining when the latter has disappeared, it has generally been necessary to make use of a device comprising mechanically controlled members such as for instance mechanically driven potentiomete'rs.

A device of the last mentioned gtype may for instance be'used to maintain a setting of the current in a lofadto alternate this current at certain moments only by aid of electrical impulses.

The described device may also be used to maintain a test value, for'instance the maximum value of a varying quantity, or to maintain a test value obtained at-a moment When'the quantity to be measureddisappears.

The'desired result according to the invention isobtained by using a'trans-ductor of which the outstanding feature is that the part of the transductor core which is-arr-a-nged to be traversed substantially only by a direct current flux is at least partly made of a material having appreciable hysteresis. This involves the considerable advantage that the transductor which is a static apparatus without movable parts and without wear may be utilized for control devices of the described type.

In the accompanying drawing Fig. 1 schematically shows a suitable transductor core with windings according to the invention. Fig. 2 shows a diagram of the load voltage as a function of the control current of a transductor having such a core. In Fig. 3 a diagram of connections is shown illustrating a form of the invention.

According to Fig. 1 the single-phase transductor illustrated consists of a three-legged core 1 provided with alternating current windings 2 and 3 arranged on the outer legs. A part 4 of the length of the central leg, which at such a core may be substantially free from alternating current flux by proper arrangements of the alternating current windings, is made of a material having a hysteresis loop of considerable width and of as rectangular a form as possible. This is attained if the said part 4 for instance consists of magnetic steel. According to the figure, the central leg is provided with two direct current control windings 5 and 6, one of which may suitably be a winding for self-excitation of the transductor. It is not necessary that the whole length of the central leg is made of magnetic steel, and if desired it may be provided with further control windings. The latter must not, however, be 'arranged 0n the central leg, the same result may be obtained by arranging them on the outer legs, and winding them in proper direction.

Z ,8 18 ,545 Patented-moon 31", 7

Fig. .zi's-hows the wide hysteresis-loop d 1 a -transdiictor in a diagram of load voltage E as a function of the totally applied control r current i; This loop-may: be: called: the

cont'rol curve ofthe transductor: Thelform of the contr'ol curve: will the highly depending on the properties of: the iron in the partof lthe;transductor:'whichdsmot"subject to an alternating current ifiux; for finstance the' central leg of a transductor according .to Fig. -l. If this"partof the core is :made of a'material wit-h liigl'ia'emanence :and 'high coercive force', the control curve will also o'btain a' for'm which is determin'ed :by the 'hysteresis' loopi of the material in the legiwhich' is free from'alternating cu'rrentflux; If according .to Fig. 2 the transductor-iscontrolled byfthe currents i +'i alongzthe 'curve A to'th'e" point B, and the control current is then d'ecreased; the loadvoltage will fall along the curve C. If t-he' transductor ispremag netized by a constant cirrrent i it is thus possible to' control the transductor" within'a comparatively large range by. means of a relatively small 'control current-i lf a control current iyafterhavingvgiven the'operating point B of the ascending;curve*-=branch A is diminished tozero, the load -voltage will only. fall to the point D-of the only slightly sloping curve' 'bran'ch C. The voltage will thus only besubject to an insignifi'cantdecrease, 'and this decrease may be-kept at a low value if the transductor'has been 'so dimensioned that 11 the remanent flux of the mag netic steel part in the legwhich is free fromaltern'ating current-flux can develop-am m. f. which isable' to' replace the control-ampereturns from the current is :when this disappears.

A connection: diagram :for: a transductor according "to the invention is'shown' in Fig.1 3 The two alternating cur rent windings 2 and 3 on the: core' :1-'Iarei in series with self-magnetization rectifiers 7, fi'con'nected inparallel in amalternatingcurrent circuit connected to terminals 9} 10 and further compri'sing :a full wave: rectifier 'lltand a load 12.:- It is already 'known that"the 'transductor' m ay be self magnetized in such a way that it will operate in an nn stable way; but 7 in :the present easeit 1 is? desired tlr'a't th e transductor is provided 1 with a selfmagnetiiatio'n which is as complete as possible to maintain the stability. If this desire is fulfilled only a few numbers of ampereturns are necessary to maintain the output voltage. In order to attain this result, a direct current is drawn from the rectifier 11 which may traverse a winding 5 which is arranged on the central leg. It is understood, however, that even other ways are available to increase the degree of selfmagnetization, for instance by arranging winding parts on the legs provided with alternating current windings so that each part is traversed by the rectified portions of the current in the alternating current winding on the opposite outer leg.

A direct current supplied from the terminals 14 is arranged to traverse a control winding 13 on the central leg or alternatively on the outer leg. This direct current serves as a premagnetization current like the current i; in Fig. 2.

The control current i (Fig. 2) may be applied to the transductor by aid of a winding 6. For controlling the transductor this winding may be fed via an adjustable resistor which is suitably so connected that positive as Well as negative control current may be obtained. It is also possible to alter the transductor output continuously by supplying the winding 6 with a current of suitable direction and duration which is applied in one or the other direction during shorter or longer time. In this case it is suitable to include time-delay means in the control circuit, for example a capacitor 15 and a resistor 16 and to arrange it so that different poles of the control current source 17 may be connected by means of one of two contacts 18 and 19. By closing the contact 18, the winding 6 will obtain a positive current according to Fig. 2, and 'by instead closing the contact 19 a so large negative current may be admitted as is necessary for the demagnetiza tion so that the operating point P on the curve branch A in Fig. 2 will be reached again after this contact has been broken.

By suitable dimensioning of the transductor and its auxiliary means according to Fig. 3 it will be possible to obtain a voltage across the load which is increased from an initially low value by closing the contact 18 which suitably should be designed with a pressure contact. The increase of voltage will then be made dependent on the time during which the button is pressed, and owing to the delay circuit it will be possible to magnetize the transductor in dependence of the time during which the button is pressed. When the button is released, the transductor will maintain an output voltage, i. e. a voltage across the load which is unchanged except for the previously mentioned relatively insignificant decrease. To diminish the output voltage the button 19 is pressed during a time which corresponds to the desired decrease of voltage.

In order to improve such a pressure button setting, the transductor or its auxiliary circuits may be provided with other delaying members by which the resetting will be slower, and by which the transductor may be controlled with a higher precision. Such delaying members may consist of a capacitor or an inductance in the control circuit, self-magnetized circuit or output circuit arranged in any way known per se. They may also consist of thermic devices, for instances thermistors. In the latter cases, the controlling of the transductor may not only be performed by pressure buttons or such members but also in other ways. A transductor of the described type may be controlled to give an output quantity which is dependent either on the duration or on the product of the duration and magnitude of a current or a voltage applied to the input side of the transductor.

I claim as my invention:

1. A transductor device comprising a multilegged core structure having windings for alternating and direct currents, respectively, means for energizing said windings, a load in circuit with said alternating current windings, means whereby said last mentioned windings are arranged to give two interlinked magnetic circuits, said core having one common 'core leg free from alternating current flux, and said direct current windings being arranged to give a direct current flux in said common core leg, at least part of the length of said common core leg consisting of a magnetic material having an appreciably larger hysteresis than the rest of the core, and control means in circuit with at least one of said direct current windings, the control action of said last mentioned winding being operative on the ascending part of the hysteresis loop of the transductor curve.

2. A transductor device according to claim 1, comprising a threelegged core structure, alternating current windings on the outer legs of the core, direct current windings on the central leg, at least part of the length of the central leg consisting of a magnetic material having an appreciably larger hysteresis than the rest of the core.

3. A transductor device according to claim 1, comprising a threelegged core structure, alternating current wind,- ings on the outer legs of the core, direct current windings on the outer legs of the core, said direct current windings being so arranged and connected as to give rise to cooperating magnetic fields in the central leg of the core, at least part of the length of said central leg consisting of a magnetic material having an appreciably larger hysteresis than the rest of the core.

4. A transductor device according to claim 1, comprising means for self-magnetization of the transductor.

5. A transductor device according to claim 1, comprising a number of direct current windings, one of which being arranged to pre-magnetize the transductor to a certain basic point, and another of which being adapted to receive a temporarily acting control current of a certain polarity, and a capacitor-resistor combination serving as a time-delay device in circuit with said last-mentioned winding.

References Cited in the file of this patent UNITED STATES PATENTS 1,910,381 Dowling May 23, 1933 1,921,703 Schmidt Aug. 8, 1933 2,465,451 Hedstrom et al. Mar. 29, 1949 2,470,556 Hedstrom et al. May 17, 1949 2,552,203 Morgan May 8, 1951 

